Method and apparatus for providing quality-of-service delivery facilities over a bus

ABSTRACT

The invention provides quality-of-service (QoS) delivery services over a computer bus having isochronous data transfer capabilities. A transmitting node on the bus transmits a message to an intended recipient indicating a requested bandwidth for a connection. If the intended recipient has sufficient resources, it allocates an isochronous data channel on the bus and notifies the transmitter of the allocated channel. Thereafter, the transmitter transmits the data on the allocated channel. If the recipient cannot allocate a channel, it does not respond, and the transmitter thereafter detects a time-out condition and begins transmitting using a “best efforts” scheme (i.e., non-guaranteed time delivery). In a second variation, a receiving node detects that it is receiving large quantities of data from a transmitting node. In response, the receiving node allocates an isochronous data channel on the bus and notifies the transmitter of the allocated channel. Thereafter, the transmitter transmits using the allocated isochronous channel. In a third variation, multiple receiving nodes that need to receive streaming data from a single transmitting node share a common isochronous data channel. In any of these variations, each receiver can periodically transmit a “deadman” timer message on a broadcast channel to indicate that it is still receiving on a given channel. If a transmitter detects that the deadman timer has expired, it reverts to transmitting data using a “best-efforts” scheme. A transmitter can transmit both to receivers that can handle QoS services and those that cannot explicitly support QoS services.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of prior U.S. patent application Ser.No. 09/829,880, filed Apr. 11, 2001 now U.S. Pat. No. 6,820,150, theentire contents of which are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates generally to providing network-typeservices over a bus, such as the IEEE-1394 serial bus. Moreparticularly, the invention provides a method and apparatus forproviding quality of service delivery facilities over such a bus.

BACKGROUND OF THE INVENTION

The well-known Transmission Control Protocol/Internet Protocol (TCP/IP)has been used for many years to transmit data between computers. Withthe advent of the Internet, increasing numbers of people are usingTCP/IP to transmit video, audio, and other forms of digital information.Applications such as videoconferencing and remote downloading of musicrely on TCP/IP to transmit large quantities of information by breakingit up into packets that are then routed through the Internet.Unfortunately, the Internet cannot guarantee delivery of the informationwithin a specified time period. Because data packets can be routedthrough many different computers depending on network trafficconditions, some packets may be delayed, causing “jerky” audio or videodata.

It is conventional to transmit Internet Protocol (IP) packets over localarea networks (LANs) such as an Ethernet. In such a scheme, IP datapackets are “encapsulated” in an Ethernet frame, transmitted over anEthernet LAN, and “unwrapped” at the receiving node to restore theoriginal IP packet. In such networks, even though the distance betweencomputers is generally much shorter than the Internet, there is no wayto guarantee delivery of a given data packet within a specified timeperiod. If the local area network becomes temporarily congested due tonetwork traffic, time-sensitive data such as video streams can bedelayed for an indeterminate time period.

One scheme for mitigating the aforementioned problem requires thatnetwork users (e.g., application programs) request bandwidth from a“Subnet Manager,” which acts as a central clearinghouse for bandwidth onthe Ethernet. Each network user must register with and use the serviceto transmit data packets. If even one network user fails to registerbefore making use of the network, the scheme can fail, since the oneuser can effectively make unfettered use of the bandwidth on thenetwork. Existing application programs must typically be modified toconform to the new scheme. Moreover, because the physical bus topologyis inherently non-deterministic (e.g., collisions can prevent a givenpacket from reaching its destination in a specified time period),packets can still arrive late, causing jitter and other effects.

Recently, a serial bus standard known as the IEEE 1394 bus has beendeveloped. Implementations of this bus are based on the internationallyadopted ISO/IEC 13213 (ANSI/IEE 1212) CSR Architecture Specification andthe IEEE 1394-1995 Serial Bus Specification. A typical system conformingto the IEEE 1394 standard includes a plurality of nodes that areinterconnected via point-to-point links, such as cables, that eachconnect a single node of the serial bus to another node of the serialbus. The nodes are addressable entities that can be independently resetand identified.

The 1394 bus provides both asynchronous and isochronous (time-guaranteeddelivery) capabilities. Up to 64 isochronous channels are available onthe bus. Nodes needing to send isochronous data must reserve bandwidthand a channel number on which to transmit. Bandwidth is measured as thepercentage of a nominally 125-microsecond isochronous interval.Reservation of bandwidth and channel numbers is performed bymanipulating registers on a well-known bus node, referred to as theisochronous resource manager (IRM).

The IEEE 1394 bus provides three primary types of bulk transfer:

(1) async-write (write to a specific address on a specific node). Thisis a point-to-point, best-effort, acknowledged service with notimeliness guarantees.

(2) async-stream (stream data on a specific channel). This is amulticast, best-effort, non-acknowledged service with no timelinessguarantees.

(3) isoch-stream (stream data on a specific channel with timeguarantees). This is a multicast, isochronous (latency under 250microseconds) non-acknowledged service that uses the same 64 channelsavailable under async-stream.

Various implementations of the IEEE 1394 bus in computer systemstypically include layered hardware and software support based ontransaction, link, and physical layer protocols. The Internet Requestfor Comments (RFC) 2734, available athttp://www.ietf.org/rfc/rfc2734.txt, describes a scheme for using the1394 bus to transmit IP datagrams. The document generally describes amulticast channel allocation protocol (MCAP), which permits managementof serial bus resources when used by IP multicast groups. However, itdoes not provide a generalized approach for providing quality-of-servicefacilities for applications using the bus.

Another document(http://search.ietf.org/internet-drafts-ietf-ip1394-ip-over-iso1394-00.txt)describes a proposal for using the isochronous channels on an IEEE1394-compliant bus to guarantee bandwidth. The document generallysuggests transmitting specific IP flows over a certain isochronouschannel on the 1394 bus. However, it does not address various QoSrequirements (e.g., point-to-point flows, such as a TCP connection), anddoes not support multicast.

Another document (IEC 61883-1) describes a protocol for the cooperativeallocation and sharing of IEEE 1394 isochronous channels amongaudio/video devices. The protocol concerns itself purely with thereservation of channels and setting maximum transmission parameters forchannels; it does not concern itself with the advertisement of the typeof data transmitted over a particular channel.

Conventional approaches for allocating bandwidth to transmit datapackets over a bus can incur various disadvantages, such as: (1) thepossibility that bus resources can be locked up indefinitely if aresource requester crashes after allocation; (2) wasteful allocationwhere a transmitting node requests resources but the intended recipientis not available or able to use the resources; (3) an inability ofapplications that lack QoS capabilities to efficiently use bandwidth onthe bus; and (4) no graceful degradation (i.e., failure to allocateisochronous facilities results in failure of communication, rather thandegraded communication).

Consequently, there is a need to provide a decentralizedquality-of-service facility that can be implemented over the IEEE 1394bus, and that can adapt to changing conditions on the bus. Moreover,there is a need to provide quality-of-service features even forapplications that do not directly support QoS services.

SUMMARY OF THE INVENTION

The invention permits applications, including those that supportquality-of-service (QoS) features (e.g., videoconferencing), to takeadvantage of guaranteed delivery features of a computer bus such as theIEEE 1394 serial bus. In one embodiment, a transmitting node on a bustransmits a message to an intended recipient indicating a requestedbandwidth for a connection. If the intended recipient has sufficientresources (e.g., a typical 1394 implementation limits each receiver tono more than 4 reception channels), it allocates an isochronous datachannel on the bus and notifies the transmitter of the allocatedchannel. Thereafter, the transmitter transmits the data on the allocatedchannel. If the recipient cannot allocate a channel, it does notrespond, and the transmitter thereafter detects a time-out condition andbegins transmitting using a “best efforts” scheme (i.e., non-guaranteedtime delivery).

In a second embodiment, a receiving node detects that it is receivinglarge quantities of data from a transmitting node on a broadcastchannel. In response, the receiving node allocates an isochronous datachannel on the 1394 bus and notifies the transmitter of the allocatedchannel. Thereafter, the transmitter transmits using the allocatedisochronous channel.

In a third embodiment, multiple receiving nodes that need to receivestreaming data from a single transmitting node share a commonisochronous data channel. In this embodiment, each receiver transmits amessage to other potential recipients to determine whether any otherrecipient has already allocated an isochronous channel. If no otherreceiver has already allocated a channel, the first receiver allocates achannel and notifies other potential recipients of the allocatedchannel. (If another receiver had already allocated a channel, thesecond receiver receives the transmission on the already-allocatedchannel.) If the first receiver that allocated the channel no longerneeds it, it keeps it allocated if any other receivers are listening tothe channel and deallocates it when no other receivers are using it.

In any of the above embodiments, each receiver can periodically transmita “keep alive” message on a broadcast channel that acts as a deadmantimer to indicate that the receiver is still receiving on a givenchannel. If a transmitter detects that the deadman timer has expired, itreverts to transmitting data using a “best-efforts” scheme. Moreover, atransmitter can transmit both to receivers that can handle QoS servicesand those that cannot explicitly support QoS services.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram of a conventional general-purposedigital computing environment that can be used to implement variousaspects of the present invention.

FIG. 2 shows a system employing a quality-of-service manager (205 and210) in each of a plurality of nodes coupled over an IEEE 1394 bus.

FIG. 3 shows method steps for allocating bandwidth in a system between atransmitting node and a receiving node according to one variation of theinvention.

FIG. 4 shows method steps for allocating bandwidth in a system between atransmitting node and a receiving node according to a second variationof the invention.

FIG. 5 shows method steps for allocating bandwidth in a system between atransmitting node and a plurality of receiving nodes according to athird variation of the invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a schematic diagram of a conventional general-purposedigital-computing environment that can be used to implement variousaspects of the present invention. A computer 100 includes a processingunit 110, a system memory 120 and a system bus 130 that couples varioussystem components including the system memory to the processing unit110. The system bus 130 may be any of several types of bus structuresincluding a memory bus or memory controller, a peripheral bus, and alocal bus using any of a variety of bus architectures. The system memory120 includes a read only memory (ROM) 140 and a random access memory(RAM) 150.

A basic input/output system (BIOS) 160 containing the basic routinesthat help to transfer information between elements within the computer100, such as during start-up, is stored in ROM 140. Computer 100 alsoincludes a hard disk drive 170 for reading from and writing to a harddisk (not shown), a magnetic disk drive 180 for reading from or writingto a removable magnetic disk 190, and an optical disk drive 191 forreading from or writing to a removable optical disk 192, such as a CDROM or other optical media. Hard disk drive 170, magnetic disk drive180, and optical disk drive 191 are respectively connected to the systembus 130 by a hard disk drive interface 192, a magnetic disk driveinterface 193, and an optical disk drive interface 194. The drives andtheir associated computer-readable media provide nonvolatile storage ofcomputer readable instructions, data structures, program modules andother data for the computer 100. It will be appreciated by those skilledin the art that other types of computer readable media which can storedata that is accessible by a computer, such as magnetic cassettes, flashmemory cards, digital video disks, Bernoulli cartridges, random accessmemories (RAMs), read only memories (ROMs), and the like, may also beused in the exemplary operating environment.

A number of program modules can be stored on the hard disk, magneticdisk 190, optical disk 192, ROM 140 or RAM 150, including an operatingsystem 195, one or more application programs 196, other program modules197, and program data 198. In particular, the RAM 150 will, from time totime, store various device drivers, as known in the art. A user canenter commands and information into computer 100 through input orselection devices, such as a keyboard 101 and a pointing device 102. Thepointing device 102 may comprise a mouse, touch pad, touch screen, voicecontrol and activation or other similar devices. Other input devices(not shown) may include a microphone, joystick, game pad, satellitedish, scanner, or the like. These and other input devices are oftenconnected to the processing unit 110 through a serial port interface 106that is coupled to the system bus, but may be connected by otherinterfaces, such as a parallel port, a game port or a universal serialbus (USB). A monitor 107 or other type of display device is alsoconnected to system bus 130 via an interface, such as a video adapter108. In addition to the monitor, personal computers typically includeother peripheral output devices (not shown), such as speakers andprinters.

An IEEE 1394 interface 140 may also be provided. The IEEE 1394 interface140 couples an IEEE 1394-compliant serial bus 145 to the system bus 130or similar communication bus. The IEEE 1394-compliant serial bus 145, asknown in the art, allows multiple devices 150 to communicate with thecomputer 100 and each other using high-speed serial channels. The IEEE1394 serial bus standard is based largely upon the internationallyadopted ISO/IEC 13213 (ANSI/IEEE 1212) CSR Architecture Specificationand the IEEE 1394-1995 Serial Bus Specification. Additional buses suchas the PCI bus can be provided in computer 100 and interfaced to theIEEE 1394 and other buses.

A typical serial bus having an IEEE 1394 standard architecture iscomprised of a multiplicity of nodes that are interconnected viapoint-to-point links, such as cables, that each connect a single node ofthe serial bus to another node of the serial bus. The nodes themselvesare addressable entities that can be independently reset and identified.Nodes are logical entities, each with a unique address. Each nodeprovides a so-called configuration ROM (read-only memory)—hereinafterreferred to as configuration memory—and a standardized set of controlregisters that can be accessed by software residing within the computersystem.

The computer 100 can operate in a networked environment using logicalconnections to one or more remote computers, such as a remote computer109. The remote computer 109 typically includes at least some of theelements described above relative to the computer 100, although only amemory storage device 111 has been illustrated in FIG. 1. The logicalconnections depicted in FIG. 1 include a local area network (LAN) 112and a wide area network (WAN) 113. Such networking environments arecommonplace in offices, enterprise-wide computer networks, intranets andthe Internet.

When used in a LAN networking environment, the computer 100 is connectedto local network 112 through a network interface or adapter 114. Whenused in a WAN networking environment, the computer 100 and remotecomputer 109 may both include a modem 115 or other means forestablishing a communications over wide area network 113, such as theInternet. The modem 115, which may be internal or external, is connectedto system bus 130 via the serial port interface 106. In a networkedenvironment, program modules depicted relative to the computer 100, orportions thereof, may be stored in the remote memory storage device.

It will be appreciated that the network connections shown are exemplaryand other means of establishing a communications link between thecomputers can be used. The existence of any of various well-knownprotocols, such as TCP/IP, “ETHERNET”, FTP, HTTP and the like, ispresumed, and the system can be operated in a client-serverconfiguration to permit a user to retrieve web pages from a web-basedserver. Procedures of the present invention to be described below canoperate within the environment of the computer 100 shown in FIG. 1.Although the invention is generally applicable to a computer operatingin accordance with the IEEE 1394 standard, it is not intended to be solimited.

FIG. 2 shows a system employing a quality-of-service manager (205 and210) in each of a plurality of nodes coupled over an IEEE 1394 busaccording to one aspect of the present invention. As shown in FIG. 2,two computer nodes 250 and 260 are coupled through a bus such as theIEEE 1394 bus. As is conventional, each node includes a 1394 hardwarecard (207 and 208, respectively) and an appropriate 1394 bus driver (206and 209, respectively) that collectively permit the nodes to communicateusing the 1394 bus.

In one embodiment, each 1394-compliant bus driver comprises an Open HostController Interface (OHCI) driver implementation of the IEEE 1394 linklayer protocol. The OHCI is described in the 1394 Open Host ControllerInterface Specification, which is widely available and well known tothose of skill in the art. This interface can transmit and receive alldefined 1394 packet formats using Direct Memory Access (DMA) to writethe packets into the host computer's memory. In various embodiments,virtual device drivers can be used to connect to and communicate overthe bus.

As is conventional, each node includes one or more application programs(201, 202, 213, and 214, respectively) that operate using TCP/IPprotocols 204 and 211. Each application program may comprise, forexample, a program that transmits audio and/or video data between nodes.As one example, one application program may comprise a videoconferencingapplication that permits two persons to see and hear each other bytransmitting audio and video packets over the bus. In this case, it maybe important or desirable to provide time-guaranteed delivery of datapackets to prevent “jerky” audio and video displays at each node.Certain videoconferencing applications maybe “QoS-enabled” in that theyare aware of bandwidth allocation procedures and can issue commands toallocate bandwidth in the network. Other applications may not have suchfeatures. In one embodiment, the present invention can also accommodatethe latter type of applications without requiring software modificationsto the applications.

For applications that are “QoS-enabled” (i.e., they includefunctionality that makes direct use of quality-of-service features suchas bandwidth allocation), a traffic control manager (TCM) component 203and 212 traps QoS calls and routes them to the appropriate functions inthe lower levels of software, as described in more detail herein. Datapackets are transmitted using TCP/IP protocols 204 and 211, as isconventional. Various features of the present invention can beincorporated into QoS managers 205 and 210, as described in more detailbelow. It may be desirable to abstract out or translate different typesof QoS requests (including conventional ones such as RSVP) into1394-specific allocation requests. Although it is contemplated that theinventive principles can be implemented using the architecture of FIG.2, other approaches are of course possible and the invention is notintended to be limited in this respect.

FIG. 3 shows method steps for allocating bandwidth in a system between atransmitting node and a receiving node according to one variation of theinvention. It is assumed in FIG. 3 that a QoS-enabled application on afirst node seeks to communicate with a QoS-enabled application on asecond node over the IEEE 1394 bus. Steps performed by the transmittingnode are shown on the left side of FIG. 3, while those performed by thereceiving node are shown on the right side of FIG. 3. It will beappreciated that for a two-way transmission (e.g., full-duplexvideoconferencing), each node will effectively act as both a transmitterand a receiver, and thus the steps shown can be replicated on oppositenodes. In one embodiment, the steps shown in FIG. 3 are performed by QoSmanagers 205 and 210 of FIG. 2. The inventive steps, however, can bepracticed in various other ways, and the invention is not limited to thestructures shown in FIG. 2.

Beginning in step 301, in response to receiving a request to transmitdata at a given data rate (e.g., a known rate sufficient to supportgood-quality video frames), the transmitting node transmits a requestfor bandwidth to the intended receiving node. The request can includerelated information such as the source IP address, port number,protocol, and destination IP address. In one embodiment, a flowdescriptor can be used to reference information pertaining to each flowand to allow an application to advertise what it is providing and whatit needs. For example, a flow descriptor may comprise fields such asTCP/IP flow information (source IP address, source port, destination IPaddress, and destination port) and, optionally, a data format (e.g.,MPEG, audio, etc.) This transmission can occur over a broadcast channelthat is used to communicate among the nodes for purposes of resourceallocation.

In step 309, the receiving node checks to determine whether resources(e.g., an isochronous channel and suitable bandwidth) are available. Forexample, in certain systems the IEEE 1394 bus may be configured topermit each node to allocate a maximum number (e.g., four) isochronousdata channels. If the intended recipient node had already allocated thismaximum number of channels, then no further resources would be availablefor allocation.

In step 310, a check is made in the intended receiver to determinewhether resources are available for the communication. If not, then instep 311 the request is ignored, and processing terminates. (If thereceiving node does not support QoS services, the request will also beignored or rejected, leading to the same or similar result). Ignoringthe request will cause the transmitter to time-out, as described in moredetail below.

In step 312, if resources are available, the receiver allocates anisochronous data channel with desired bandwidth. In one embodiment,these resources are allocated using conventional IEEE 1394-specificfunction calls.

In step 313, the receiving node transmits a message on the broadcastchannel to the transmitting node indicating the allocated channel numberand bandwidth. Thereafter, the receiving node periodically transmits a“keep alive” message in step 314 to the transmitting node indicatingthat the resources are still allocated. In step 315, the receiverreceives data from the transmitter over the allocated isochronous datachannel. In step 316, the receiver checks to determine whether thetransmitting node has transmitted a similar periodic “keep alive”message. If such a message is received, then processing continues instep 314 until such messages are no longer received. If no such “keepalive” message is received within a time-out period, then in step 317the resources are deallocated, and the transmitter is optionallynotified of the deallocation.

The “keep alive” timer scheme described above allows for systemresources to be automatically deallocated in the event that one of thenodes (e.g., the transmitter or receiver) fails, thus preventingresource lock-up.

Returning to the left side of FIG. 3, if in step 303 no response isreceived from the intended recipient within a timeout period, then instep 304 communication will revert to a “best efforts” transmissionscheme, which does not require allocation of bus resources. For example,the transmitting node can transmit the data packets using asynchronouswrites over the 1394 bus. Alternatively, the transmitting node cantransmit the data packets using asynchronous streams on a specific datachannel. The latter scheme provides non-acknowledged service with notimeliness guarantees. This default to a best-efforts transmission modeprovides a degraded communication mode that permits the nodes tocommunicate even if bus resources are not available, rather thanreturning an error message to the application program.

In step 303, assuming that a response was received from the intendedreceiver (i.e., no time-out), then in step 305 the transmitter beginstransmitting data using the allocated resources (e.g., using theallocated channel and bandwidth parameters). In step 306, thetransmitter periodically transmits a “keep alive” message to thereceiver in order to signal that the allocated channel is still in use.If in step 307 the transmitter determines that a similar “keep alive”message has not been received from the receiver within a certaintime-out period, then in step 308 communication reverts to a “bestefforts” transmission mode as described above. In one variation, thetransmitter can attempt to later re-establish guaranteed deliverycommunication with the intended receiver after a time-out period.Assuming that the receiver and transmitter continue to transmit “keepalive” messages for the resources, the transmitter transmits data usingthe allocated resources.

One advantage to the above-described scheme is that a QoS-enabledapplication can communicate with a non-QoS enabled application over thebus. For example, if a QoS-enabled transmitting node attempts toallocate bus resources to transmit streaming video packets, but thecorresponding application at the receiving node is not QoS-enabled, thenthe transmission can automatically proceed in a degraded mode usingbest-efforts communication. This is advantageous over a scheme thatwould otherwise not allow incompatible transmitting and receiving nodesto communicate.

FIG. 4 shows method steps for allocating bandwidth in a system between atransmitting node and a receiving node according to a second variationof the invention. In contrast to the scheme shown in FIG. 3, where it isassumed that the transmitting node is QoS-enabled (i.e., it makes anexplicit request to allocate bus resources), the embodiment of FIG. 4works even where the transmitting application is not QoS-enabled. Inthis embodiment, a high traffic condition is automatically detectedbetween the nodes, and an isochronous data channel is automaticallyallocated and used to transfer further data packets between the nodes.As with the embodiment of FIG. 3, the steps in FIG. 4 can be carried outin QoS manager 205 and 210 of FIG. 2, preferably in a data link layer ofa protocol stack.

Beginning in step 401, an application program begins transmitting datapackets over the bus, such as over a broadcast channel or over anasynchronous data channel. In step 407, the receiving node beginsreceiving the data packets and determines that a large number of packetsare continually being received from the transmitting node. (This can befurther refined to detect not only traffic from a particular node, buttraffic occurring over a specific IP flow, such as from a particular IPaddress). In response to this determination, the receiver in step 408allocates an isochronous data channel on the bus with sufficientbandwidth to support the expected data packets, and maps the datachannel to the particular flow (e.g., the IP addresses from which thepackets are being received). In step 409, the receiving node notifiesthe transmitting node of the newly allocated isochronous data channel.Steps 410 through 413 are similar to steps 314 through 317 of FIG. 3 andno further elaboration is required.

Returning to the transmitting side of FIG. 4, in step 402 thetransmitting node detects the assignment of a new data channel for thedesignated flow, and in step 403 changes its transmission mode to begintransmitting the packets associated with the flow over the newlyallocated isochronous data channel. In step 404, the transmitterperiodically transmits a “keep alive” message to the receiver to signalthat the resources are being used. In step 405, the transmitterdetermines whether a similar periodic “keep alive” message has beenreceived from the receiver and, if not, reverts to the broadcast channelmode of communication in step 406.

As explained above, one advantage of the method shown in FIG. 4 is thattime-bounded data transmission can be used even where applicationprograms are not QoS-enabled. That is, the isochronous data channels canbe used efficiently in the system even where application programs arenot knowledgeable about such channels.

FIG. 5 shows method steps for allocating bandwidth in a system between atransmitting node and a plurality of receiving nodes according to athird variation of the invention. In the embodiment of FIG. 5, it isassumed that a single transmitter transmits data packets, and twodifferent receiving nodes seek to receive the same data stream from thetransmitter. As one example, a video broadcast (e.g., a TV program) isto be transmitted from a central node, and multiple recipient nodes seekto receive the same broadcast.

Steps 501 and 502, shown in abbreviated form in FIG. 5, are assumed toencompass steps such as those shown in FIG. 3 or FIG. 4. In other words,the transmitting node and the first receiving node set up an isochronouscommunication channel using techniques such as those illustrated in FIG.3 or FIG. 4.

In step 507, it is assumed that an application program in a secondreceiving node seeks to receive the same packets transmitted from thetransmitting node. If a TV program is being transmitted using a known IPaddress, for example, the second receiving node can determine that sucha broadcast is currently being transmitted over the bus.

In step 508, the second receiving node broadcasts a request over the busfor information regarding the flow corresponding to the transmittedpackets. This request is received by the first receiver which, in step504, checks its internal allocation tables to find the correspondingchannel information for the flow. In step 505, the first receiving nodesets a flag indicating that the channel is now being shared by a secondnode, and in step 506 transmits the flow mapping information (e.g., thechannel and bandwidth information corresponding to the requested flow)to the second receiving node.

In step 509, the second receiving node waits for a response to therequest for information. In step 510, if no response is received withina time-out period, then in step 511 it is assumed that no other node hasallocated resources for the flow, and the node proceeds to allocateresources and receive the transmission over the allocated resource.Alternatively, if a response was received from the first receiving node,then in step 512 the second receiving node begins receiving data on theshared channel.

In one embodiment, the first receiving node sets a flag indicating thatthe channel is shared (see step 505) in order to prevent thede-allocation of the resource if another node is using the sharedchannel. For example, if the user at the first receiving node terminatesviewing of a video program, first receiving node should first check tosee whether any other nodes are sharing the channel before deallocatingthe resources. If another node continues to share the channel, the firstreceiving node can continue to leave the resources allocated untileither receiving a termination request from the other node(s), or untila “keep alive” message (not shown) is no longer received from the secondnode.

Thus has been described a system and various methods for implementingquality-of-service facilities such as guaranteed time delivery of datapackets in a system, even for application programs that are notQoS-enabled. The system and methods can be used in any number ofapplications such as videoconferencing, music downloading, Internetbrowsing, and the like. The inventive principles can be practicedwithout requiring a central resource flow allocation manager, thusproviding a fail-safe and robust system.

What has been described above is merely illustrative of the applicationof the principles of the present invention. Other arrangements andmethods can be implemented by those skilled in the art without departingfrom the spirit and scope of the present invention. Any of the methodsof the invention can be implemented in software that can be stored oncomputer disks or other computer-readable media for execution in a hostor target computer. While an electrical medium has been described as thecommunications channel, the principles can also be applied using RF,fiber optic, or other media. No claim should be interpreted to be inmeans plus function format. Numbered steps in method claims should notbe interpreted to require a particular ordering of the steps.

1. A system for delivering data packets comprising: a bus configured tosupport isochronous and asynchronous modes of data transmission; atransmitting node configured to translate a bus-generic request for aquality-of-service connection into a bus-specific request fortime-guaranteed delivery services and transmit the bus-specific requestover the bus; and an intended receiving node on the bus configured toreceive the bus-specific request, determine whether sufficient resourcesare available to allocate an isochronous data channel on the bus and, inresponse to such availability, allocate the isochronous data channel andnotify the transmitting node of the allocated isochronous data channel,wherein the transmitting node transmits data packets to the intendedreceiving node using the allocated isochronous data channel, sets atimer and, in response to detecting a time-out condition based on thetransmitted bus-specific request transmits the data packets to theintended receiving node using the asynchronous delivery mode.
 2. Thesystem of claim 1, wherein the transmitting node transmitting datapackets to the intended receiving node using an asynchronous streamingdelivery mode.
 3. The system of claim 1, wherein the transmitting nodetransmitting data packets to the intended receiving node using anasynchronous write operation mode.
 4. The system of claim 1, wherein thetransmitting node transmits to the intended receiving node a “keepalive” message indicating that the transmission is continuing, andwherein the intended receiving node monitors the “keep alive” messageperiodically transmitted by the transmitting node and, in response todetecting that the “keep alive” message is no longer being periodicallytransmitted, deallocates the bus resources.
 5. The system of claim 1,wherein to the bus is an IEEE-1394 serial bus.
 6. The system of claim 1,wherein the transmitting node transmits the bus-specific request inresponse to a quality-of-service request made by an application program.7. A system of delivering data packets comprising: a bus configured tosupport isochronous and asynchronous modes of data transmission; atransmitting node configured to translate a bus-generic request for aquality-of-service connection into a bus-specific request fortime-guaranteed delivery services, and transmit the bus-specific requestover the bus; and an intended receiving node configured to receive thebus-specific request, determine whether sufficient resources areavailable to allocate an isochronous data channel on the bus and, inresponse to such availability, allocate the isochronous data channel andnotify the transmitting node of the allocated isochronous data channel,wherein the transmitting node transmits data packets to the intendedreceiving node using the allocated isochronous data channel;periodically transmitting from the intended receiving node a “keepalive” message indicating that resources have been allocated; and thetransmitting node monitors the “keep alive” message periodicallytransmitted and, in response to detecting that the “keep alive” messageis no longer being transmitted, reverts to a mode wherein the datapackets are transmitted to the intended receiving node using theasynchronous delivery mode.